Make chicken stock and pour everything in a large stock pot except milk. Cook for 2-1/2 to 3 hours and stir frequently. It's done when the rigatoni looks like dough :) If it is too thick for your taste, add some milk. I have made it both ways. Milk doesn't affect the taste, just the thickness. This recipe makes a TON so, consider halving it if you don't want leftovers.